It is an aim to reduce the temperature at a pilot burner face inside a combustor of a gas turbine and to reduce the emissions, such as nitrogen oxides NOx and/or carbon monoxide CO. The temperatures inside the combustion chamber cause higher CO and NOx emissions. In particular, inside the combustor, the mixing of fuel and gas (air) is considered as the critical issue in reducing the temperature and thereby in reducing the emissions.
Generally, a combustor comprises a swirler through which the fuel is injected typically in more than one stream e.g. as main fuel and pilot fuel. A pilot fuel is injected typically by a pilot burner, generally with a direction along a centre axis of the combustor, wherein the pilot fuel is used for controlling the combustor flame in which the main fuel in burned. The injected pilot fuel generates a predefined flame shape inside the combustor. The main fuel stream is provided via the swirler in a generally tangential direction into the combustor with respect to the centre axis of the combustor. The injected main fuel stream and the pilot fuel stream may be a liquid fuel or gaseous fuel. The combustion is achieved by a substantially non-combustible gas flow comprising an oxidant, first being mixed together with the fuel in the burner.
A high fuel concentration in the mixture of the gas, e.g. air and fuel inside the combustion chamber at the centre of the pilot burner close to the pilot face, may occur due to a back-circulation of the injected gas and fuel. Hence, it is an aim to reduce the concentration in the fuel rich mixture at the centre of the burner close to the pilot face and locate a reaction zone, where the ignition of the flame occurs, farther away from the pilot burner face to reduce high pilot burner temperatures.
WO 2009/056425 A2 discloses a combustor for a gas turbine which comprises a combustor with a burner head, a burner face and a radial swirler. The main fuel is injected through a swirler to a centre of the combustion chamber. Pilot fuel nozzles which are attached to the pilot face inject pilot fuel into the combustion chamber. A pilot fuel is injected with an individual swirl direction and with a predefined injection angle in order to modulate a desired flame profile inside the combustion chamber.
U.S. Pat. No. 5,267,442 A discloses a fuel nozzle with an eccentric primary circuit orifice. A fuel nozzle which includes an air swirler injects fuel directly to a prefilming surface of an air swirler.
U.S. Pat. No. 5,761,906 A discloses a fuel injector swirler arrangement comprising a shield element for generating fuel rich pockets in a gas or liquid fuel turbine. A stream of air is supplied through a swirler to a centre of the combustion chamber, wherein the stream of air is mixed with fuel which is injected by nozzles inside the swirler. Furthermore, shield means shields a supply of fuel from the air stream in at least one region of the injector arrangement such that fuel rich pockets of fluid are formed.